Guessing she somehow got the demon to have soooo much fun with her, through so many ways, using his body, magic devices, tools, some phallic stuff, bouncing on her boobs, using her body as his own personal jungle-gym, playing with her breasts, doing all sorts of “target practice” [magic-wise, utility-wise, & body-wise] with her entire body; using her body as an entire set of playground equipment, using her body as a bouncy castle, jumping on her back, her boobs, her butt; doing practically each & every form of aerobics imaginable, [flips, back-flips, rolls, cartwheels, & much more] on, in, and under every part of her body, and using so many tools, parts, utilities, and anything that vilga or the demon could find around the entire castle, making sure to keep her securely tight and nearly immobile [with the exception of her mouth, face, hands, and feet, but unable to escape her bondage for … at least ten entire weeks.

If she wanted, Vilga could get under, behind, beside her, and/or otherwise position herself in just the right way so that when the witch had some sort of fit or action of being extremely upset, angry, or mad, and acted like a kid, pounding her fists on the ground, stomping her feet, shaking her knees up and down [on the ground], and maybe also headbutting the ground [or some part of the wall or another part of the room] [just depending on how Vilga decided to pose her while casting some form of time freezing spell or freezing the bad witch [not in ice, just in place], instead of hitting the ground or wall [or wherever] with her fists, feet, knees, head, or other random body part, she would instead [unintentionally pleasurably, titillating, enticingly, sexually, erotically, sensually, and hotly] pound upon some [and/or each / every / all] arousing, sexual, sexy, enticing, and [eventually, after hours upon hours] ecstatic, titillating, wild, exciting, explosive, and intense orgasm-inducing part[s] of Vilga’s body.

Maybe she could cast a spell on the witch’s head so that, even when her body is locked very securely, the witch can still stretch her neck to reach her head to random things and parts of another’s body, … [but not for purposes of the witch’s own personal evil gains, only for the sole purposes of her own [and her captor’s] [sexual / sensual / erotic / carnal / fetishistic] pleasure, eroticism, carnality, and so forth. She could cast a spell on her [her own and/or the witch’s] breasts, vagina, cleavage, rack, ass, etc., … for the purposes of enlargement, shrinkage, heat, cold, change in temperature, change in sensitivity, changes in shape, changes in dimensions, changes in hardness [and softness], changes in texture, changes in ability, changes in taste, changes in scent, changes in buoyancy, changes in perkiness, … and changes in the ease, length, intensity, effect, [etc.] of orgasm, pleasure, carnality, and eroticism.

She could cast a spell that makes the witch more naive, bimbo-like, air-headed, or stupid.
She could cast a spell that makes the witch hotter, bustier, and more agreeable to, open to, excited about, suggesting of, crazy about, wild about, excited by, turned on by, sexually knowledgeable, erotically strong, sexually powerful, busty, and sexually hot from, and even loving of sex acts, sexual acts, sexually suggestive acts, sensual acts, erotic actions, etc. [of every method and sort] between her and beings of other species, mythical beings, beings of her own species, fictional objects [which become real simply from either the witch thinking about them or Viiga maybe deciding to make real for just such a situation], inanimate objects, animate objects, herself, etc]. Maybe the spell causes the effect to increase 100% with each time she does, hears, tastes, feels, sees, or otherwise experiences any type of sex, sex act, sexual act, erotic action, aphrodisiac, or sexual or sexually suggestive [in looks, use, scent, feel, name, or any other aspect] food, toy, utility, tool, or action.

She could cast a spell where every act of sex she experiences gets her more sexually powerful for the next time she has sex with that person or being.

She could cast a spell that makes the wicked, evil, lame, mean, and naughty witch learn a lesson about good manners, friendship, love, happiness, having fun, playfulness, and excitement with each sexual act, catcall, wolf whistle, slap on the ass, or sexual, sexually suggestive, erotic, or sensual action, gaze, food, utility, etc. that she does, hears, eats, feels, smells, sees, or otherwise experiences.

While she’s at it, Vilga might even decide to get the demon in on some of the action [doing every form of sex, sexual action, etc. she can think of doing to him, [and luckily, she has quite a worldly, widespread, crafty, vivid, and even overactive imagination, mind, knowledge, and experience of the sexual nature.

She might get him to pose himself somewhere so that both of them can have erotic actions with the witch at the very same time. She could do every sex act to the witch she could think of, as well.

[these are not suggestions, just a fantasy.]
Also, with every non-naughty spell she casts on the witch, she could cast that same spell on the demon.